[SPARK-3437][BUILD] Support crossbuilding in maven.

This patch get rid of _2.10 in the artifact ids and adapts the install plugin to include it instead.
This will make it easy to cross build for scala 2.10 and 2.11.

There was no way(I know) to avoid copying the same code everywhere. (Maven oddities... )
It goes without saying, but this introduces a sort of 'incompatibility' at the Maven level. Downstream projects have to change artifact _and_ version when selecting between this and a future version with different artifact names. This doesn't automatically harmonize the Spark build with the version of Scala you're using, and Maven can't resolve dependency conflicts across differently named artifacts. These are kind of inevitable.

If an end goal is to publicly support Scala 2.10 and 2.11 simultaneously, then we still have to have several published artifacts at once right? this is what `classifier` could be used for. But I suppose it's worth asking if that's the intent? or is this going to may be happen all at once for Spark 2.x?